NumPy 2 compatibility

[tovrstra]

IOData (or some of its unit tests) are not compatible with NumPy 2.0, which was released recently. Some tests fail, as can be seen in #339

At first sight, all test failures are due to the same problem:

>       return np.array(array, copy=False, dtype=dtype)
E       ValueError: Unable to avoid copy while creating an array as requested.
E       If using `np.array(obj, copy=False)` replace it with `np.asarray(obj)` to allow a copy when needed (no behavior change in NumPy 1.x).
E       For more details, see https://numpy.org/devdocs/numpy_2_0_migration_guide.html#adapting-to-changes-in-the-copy-keyword.

This should be easy to fix.